This project focuses on basic and applied research on human retroviruses, HIV-1 and HTLV-I. It covers three broad areas: I) basic research studying the regulated expression of HIV-1; II) basic research on cellular transformation events as related to HTLV-I; and III) applied research towards developing HIV-1-based vectors and designing molecular ribozymes targeted against HIV-1.Some notable scientific findings from our research program in 1999-2000 include: 1) the elucidation of a mechanism for suppression of p53-function; 2) the definition of a virally-encoded factors that selects against HIV-1 CXCR4-tropism; 3) the characterization of cellular factors that are influenced by HTLV-I in enforcing cell cycle progression; 4) the elucidation of cGMP-signaling pathway in HIV-1 LTR expression; 5) the characterization of a novel Tax-binding protein that has an AP-1-activating phenotype.